Process of producing cyclopropane



Patented Dec. 14,1931

, 4 2,102,556 UNITED STATES PATENT OFFICE 2,102,550 raocess or rsonucmo OYCLOPROPANE Henry B.

W. Giuesenkamp, Purdue Research Bass, West Lafayette, 1nd,, and Earl Dayton, Ohio, 'assignors to Foundation, West Lafayette,

Ind., a corporation oi Indiana No Drawing. Original application June is, 1936,

Serial No. 85,048. Divided and this application November 2, 1937, Serial No. 112,316

a claim. (Cl. 260-167) It is the object of this invention to produce cyclopropane rapidly and cheaply from 1,3-dichloropropane (trimethylene chloride) and zinc.

This present application is a division of copending application Serial No. 85,048,1lled June In the co-pending application of Hess and I Hinds, Serial No. 717,429, filed March 26, 1934, a synthesis of cyclopropane from 1,3-dichloropropane and zinc is disclosed. That synthesis is shown by the following summarizing equation:

successful, and can be made' to give fairly good yields of cyclopropane, yet the reaction is quite slow, and that slowness is a serious drawback to commercial operation.

By the present invention it has been found-possible by varying the procedure to obtain a number of advantages. Among such advantages are an increased speed of reaction, an increased yield of cyclopropane, a lower temperature of reaction, and the elimination of the necessity of avoiding compounds containing hydrogen replaceable by zinc.

The procedure or the present application is based on a three-fold discovery:

a. l-chloro-Zi-iodopropane and 1.3-di-iodoprbpane (trimethylene iodide) react with zinc very rapidly, even at temperatures only slightly ex-- ceeding room temperature, to give good yields of cyclopropane, and to do so even in the presence of such solvents as alcohol which contain replaceable hydrogen. Thesummariziug reactions are as iollows:

and 1,8-di-iodopropane respectively, as shown by the following reactions:

'(4) cram-cm-cmcw SNaI-wHsI CI'B-CHJ-i-WaCi Suitable solvents for carrying out this reaction are acetone and ethanol; since sodium iodide is soluble in those solvents, while sodium chloride is practically insoluble in them and so when formed is removed from the reaction by precipitation. The reactions shown by Equations 4 and 5 are in marked contrast to the reaction of most dihaloparaflinswith sodium iodide; for such reactions usually proceed in' the manner illustrated I in thefollowing equation for 1,2-dichloroeth'ane: v

It may be that the reactions shown in Equations 4 and 5 are merely summarizing reactions. and it is believed that that is the case. It is believed that what actually. happens is that the sodium iodide ionizes to yield free iodide ions which are present in the solution of sodium iodide in alcohol, and that it is these iodide ions which react with the 1,3-dichloropropane, as shown by the following equations:

The chlorine ions (01-) and the tree sodium ions (Na+) form sodium chloride, which by reason of its insolubility in the alcohol forms a precipitate and so disappears from the reaction.

The zinc chloroiodide or zinc iodide' which is formed by Equation 2 or Equation 3 apparently ionizes very little, if at all, under these conditions,

so that it produces at most only slight concensodium iodide was added. In consequence, in order to accelerate the reaction by the mere addition of sodium iodide it is necessary to employ large quantities of sodium iodide; and that makes the process prohibitively expensive.

0. However, it is possible to regenerate sodium iodide. or the iodide ions therefrom, in the reaction, by the use of a much cheaper reagent; so

that such sodiumiodide takes on the nature-oi a catalyst rather than a reactant in the total reaction, and only a small quantity of sodium iodide need be used. This regeneration is obtain-'- able by any reagent which is capable oi'reactin'g with zinc iodide to yield a more highly ionized this. Two simple ones are sodium carbonate and acetamide.

The reactions of zinc chloroiodide and zinc iodide respectively with sodium carbonate may be represented as follows:

The reactions of acetamide, which involve its use in molten form as the solvent for the main reaction, are as follows:

It is believed that the reaction with acetamide somehow results in a very great increase in the concentration of the iodide ions under these conditions; although it is not certain whether that is due to its 'forming a complex compound with zinc halides or to the fact that it is an ionizing solvent.

This three-fold discovery has several results in actual practice:

Cyclopropane may be produced by the simple reaction of zinc with either 1-chloro-3-iodopropane or 1,3-di-iodopropane as shown in Equations 2 and 3. This is a new reaction so far as is known; for although 1,3-dibromgpropane (trimethylene bromide) has been used to react with zinc to yield cyclopropane, and 1,3-dichloropropane (trimethylene chloride) has been so used as set forth in the aforesaid Hass and-Hinds copending application Serial No. 717,429, the use of 1-chloro-3-iodopropane or 1,3-di-iodopropane (trimethylene iodide) with zinc has not been suggested so far as is known.

The main advantage of the aforesaid threefold discovery, however, is inthe combination oi the three features thereof to obtain a rapid production of cyclopropane from 1,3-dichloropropane by first converting it into 1-chloro-3-iodopropane and/or 1,3-diiodopropane by the use of free iodide ions, and then reacting the products so obtained with zinc, while at the same time regenerating in the solution the iodide ions to maintain the reaction rate without requiring sodium iodide in more than catalytic amounts.

.An'example of this latter process will show the general technique. 300 gm. of acetamide, 0.02 mole oi sodium iodide, 0.377 mole of sodium carbonate, and 1.1 moles oi zinc dust are placed in a l-liter three-neck round-bottom flask fitted with a mercury-seal stirrer, a dropping funnel, and a reflux condenser in the respective necks. The reflux condenser is connected at the top to an outlet tube leading to the apparatus for collecting the gas. Any suitable means may be used to remove any ammonia which results from the reaction of traces oi moisture with the-acetamide. A charge of 0.832 mole of 1,3-dichloropropane is placed in the dropping funnel, and admitted to the body of the flask drop by drop over a period or about flve hours while the temperature of the flask is maintained at about 125 (Lt-desirably within 5 of that temperature. The gaseous product which passes from the top of the reflux condenser and is collected in the collecting apparatus is cyclopropane, which after purification boils between -34.6 and 34.1 C. (uncorrected). The yield is usually of the order of to of the theoretical yield.

Another example of this invention is as follows:

An apparatus is used consisting of a 500 ml. round-bottom 3-neck flask, a condenser, and a motor-driven-mechanical stirrer. By means of glass tubing, gases are conducted from the top of the condenser through a trap kept at -20 C.

and into a straight tube condenser kept in a. bath at about -79 C.

This flask is charged with 120 ml. of 75% aqueous ethanol, 0.1 mole of 1,3-dichloropropane, 0.1 mole of anhydrous sodium carbonate, 0.2 mole of zinc dust, and l/60 mole of sodium iodide. The flask containing this charge is heated on the steam bath for twelve hours, and about 4.0 g. of crude cyclopropane is usually evolved and collected. This is of theory.

The procedure outlined in the present application, so far asit is concerned with the preparation of cyclopropane merely by reacting zinc with 1,3-dichloropropane in the presence of iodide ions, as from sodium iodide, when no regeneration of the iodide ions is involved, is claimed in the parent application of this present divisional application, which parent application is Serial No. 85,048.

The invention claimed is:

1. The process of producing cyclopropane, which consists in bringing 1,3-dichloropropane and zinc together in the presence of sodium iodide and of a compound capable of increasing the effective concentration of iodide ions.

2. The process of producing cyclopropane, which consists in bringing 1,3-dichloropropane and ride together in the presence of iodide ions and of a compound capable oi' increasing the effective concentration or iodide ions.

3. The process of producing cyclopropane, which consists in bringing 1,3-dichloropropane and zinc together in the presence of sodium iodide and of a compound which is capable of reacting with zinc iodide to yield a more highly ionized iodide.

4. The process of producing cyclopropane,

which consists in bringing 1,3-dichloropropane and zinc together in the presence of iodide ions and of a compound which is capable of reacting with zinc iodide to yield a more highly ionized iodide.

5. The process of producing cyclopropane,-

which consists in bringing 1,3-dichloropropane and zinc together in the presence of sodiumiodide and of sodium carbonate.

6. The process of producing cyclopropane, which consists in bringing 1,3-dichloropropane and zinc together in the presence of iodide ions and of sodium carbonate.

'7. The process of producing cyclopropane,

which consists in bringing 1,3-dichloropropane and zinc together in the presence of sodium iodide and ofacetamide. v 8. The process of producing cyclopropane, which consists in bringing 1,3-dichloropropane and zinc together in the presence of iodide ions and of acetamide.-

- HENRY B. HASS.

EARL W. GLUESENKAMP. 

